The present invention relates to thrombin inhibitors that are useful as anticoagulants. In particular, the present invention is directed to peptide derivatives having high antithrombotic activity and high oral bioavailability as well.
Thrombosis, excessive blood clotting, plays a significant role in cardiovascular and related diseases, and thrombotic events underlie a significant proportion of the mortality and morbidity associated with cardiovascular disease. This thrombosis causes a range of significant disease states which are characterized by the location of the blood vessel in which the clot is formed.
Thrombin is a trypsin-like serine protease that plays a key role in the blood coagulation cascade by catalyzing the conversion of fibrinogen to insoluble. This enzyme also activates factor V and factor VIII for its own production and potently activates platelets as well. Therefore, thrombin has long been recognized as a central regulator in thrombosis and hemostasis, and its inhibition has become a major therapeutic target in the treatment of cardiovascular diseases such as myocardial infarction, unstable angina, deep vein thrombosis and pulmonary embolism.
Indirect thrombin inhibitors such as heparin and warfarin (coumarin) have been used as antithrombotic therapies with, however, several limitations. Heparin demonstrates low bioavailability and is associated with side effects such as bleeding problems, moreover, it is not able to inhibit clot-bound thrombin. Warfarin is an effective oral anticoagulant but it has a narrow therapeutic window and also requires patient monitoring. A natural protein inhibitor, hirudin, has been associated with bleeding complications.
Most of low molecular weight thrombin inhibitors are broadly based upon peptides or peptidomimetic templates which operate by a direct mechanism of action against the target enzyme. Early examples are tripeptidic aldehydes such as D-Phe-Pro-Arg-H and Me-D-Phe-Pro-Arg-H that have been reported to be effective thrombin inhibitors (Bajusz et al. J. Med. Chem. 1990, 33, 1729).
Recently, D-Phe-Pro-Agmatine and its derivatives have been described as thrombin inhibitors in U.S. Pat. No. 4,346,078 and WO 93/11152 (agmatine: 1-amino-4-guanidinobutane). These compound are different from the earlier tripeptidic compounds in that the agimatine compounds lack a carbonyl moiety found in similar compounds containing an Arg side chain.
More recently, certain tripeptidic thrombin inhibitors in which 4-amidinobenzylamine is incorporated at P1 position in place of agmatine, have been disclosed (WO 94/29336, WO 95/23609, WO 96/17860, WO 96/24609, WO 96/25426). These amidine-based compounds possess in most cases mono-substitued D-alanine and D-glycine such as phenylalanine, cyclohexylalanine, and cyclohexylglycine. Good antithrombotic activity of this class of compounds is also reported (WO 95/23609).
Certain tripeptidic thrombin inhibitors bearing di-substitued D-alanine (i.e. D-diphenylalanine) at P3 position and non-amidine P1 moieties have been disclosed (WO 93/11152, U.S. Pat. No. 5,510,369, WO 97/15190). These compounds have been reported to have higher potency against thrombin compared to the corresponding mono-substitued D-alanine alalogs (i.e. D-phenylalanine) (J. Med. Chem. 1992, 35, 3365; J. Med. Chem. 1997, 40, 830). In addition, some of this class of compounds exhibited good oral bioavailability (J. Med. Chem. 1997, 40, 3687; J. Med. Chem. 1997, 40, 3726).
Very recently, certain tripeptidic thrombin inhibitors bearing both D-diphenylalanine at P3 position and 5-membered-aryl amidine (e.g. thienylamidine) at P1 side chain have been disclosed (WO 00/39124). This class of compounds exhibited high antithrombotic activity and high oral bioavailability as well.
Therefore, there is a need in the art for thrombin inhibitors which have improved oral bioavailability and stablility as compared to those described supra. The present inventors have found that the compounds of the present invention, as defined below, are potent inhibitors of thrombin in vitro and in vivo. In particular, the compounds of the present invention exhibit high bioavailability after oral administration.
It is an object of the present invention to provide compound of the following chemical formula (I) which modulate and/or inhibit the serine protease thrombin, as well as acceptable prodrugs, pharmaceutically active metabolites, and pharmaceutically acceptable salts thereof (hereinafter, such compounds, prodrugs, metabolites and salts are collectively referred to as xe2x80x9cagentsxe2x80x9d). Other objects of the present invention are to provide pharmaceutical compositions containing the compound of formula (I) and to provide their therapeutic use in treating diseases mediated by thrombin, such as myocardial infarction, unstable angina, deep vein thrombosis and pulmonary embolism, as well as other disease states associated with blood clotting and associated clotting factors.
The above objects of the present invention are achieved by providing compound of the following chemical formula (I) 
and pharmaceutically acceptable salts thereof
wherein
n is 1 or 2;
A is hydrogen, C1-6 alkyl, aryl, xe2x80x94SO2R1, xe2x80x94PO(OC1-6 alkyl)2, xe2x80x94PO(C1-6 alkyl)2, xe2x80x94CO(C1-6 alkyl), xe2x80x94C2R2, xe2x80x94(CH2)mCO2H or xe2x80x94(CH2)mCO2(C1-6 alkyl),
wherein
R1 is hydrogen, C1-6 alkyl, C3-7 cycloalkyl, aryl, xe2x80x94(CH2)maryl or xe2x80x94NR3R4 
R2 is C1-6 alkyl, C3-7 cycloalkyl, aryl, xe2x80x94(CH2)maryl or alkenyl, and
m is 1, 2 or 3,
wherein
aryl is unsubsituted, substituted phenyl or 5-6 membered aromatic heterocyclic ring, and
R3 and R4 are independently hydrogen, C1-6 alkyl or C3-7 cycloalkyl;
B is hydrogen;
C and D are both xe2x80x99phenyl unsubsituted or substituted with one or two substituents selected from C1-4 alkyl, C1-4 alkoxy, methylenedioxy, halogen, hydroxy and NR4R5, or
C3-7 cycloalkyl;
E, F, G, and H are independently CR5 or N
wherein
R5 is hydrogen, C1-4 alkyl, C1-4 alkoxy, CF3, halogen, hydroxy or xe2x80x94NR4R5; and
I is xe2x80x94C(NH)NH2, xe2x80x94C(NH2)NOH, or xe2x80x94CH2NH2.
Another object of the present invention is achieved by providing pharmaceutical compositions comprising: an effective amount of an agent selected from compounds of Formula (I) and pharmaceutically acceptable salts, pharmaceutically active metabolites, and pharmaceutically acceptable prodrugs thereof, and a pharmaceutically acceptable carrier or vehicle for such agent. The present invention further provides methods of treating cardiovascular diseases such as myocardial infarction, unstable angina, deep vein thrombosis and pulmonary embolism, as well as other disease states associated with excess thrombin.
The present invention is further explained in more detail hereinbelow.